Indus, Brahmaputra and Ganga among the top 10 plastic waste carrying rivers

Out of the ten rivers that drain over 90% of the total plastic debris into the sea globally, there are three flowing through India – the Indus, Ganga and Brahmaputra.

While the Indus carries the second highest amount of mismanaged plastic debris to the sea, both Brahmaputra and Ganga together carry the sixth highest.

These plastic wastes originate not only from cities but also from villages along these riverine systems.

Floating polyethylene terephthalate (PET) bottles, plastic bags and even toys have become a part of the marine environment in recent times. Pitiful photographs of such plastic debris washed ashore on remote shorelines have frequently made headlines. Many beaches around the world are rimmed with mounds of plastic waste.

Most of this plastic pollution is attributed to an increase in tourism, shipping and fishing activities. But according to a recent study, a considerable portion of plastic garbage afloat in the open waters originates on land, and is drained into the seas by rivers.

Christian Schmidt and Stephan Wagner of the Helmholtz Centre for Environmental Research in Leipzig, Germany estimate that 57 of world’s rivers ferry between 0.4 and 40 lakh tonnes of plastic waste down to the open oceans every year. Just ten of these rivers are responsible for nearly ninety percent of the plastic debris drained into the oceans. Three flow through India: the Indus, the Ganga and Brahmaputra.

The study also finds that a combination of large rivers and huge populations along their banks are together responsible for unusually high amounts of untreated plastic waste going into the oceans.

“Any action to reduce plastic in these rivers would be highly effective to reduce the total riverine inputs into the oceans,” says Schmidt, the lead author of the study.

Accounting for the oceans’ plastics

A previous study had estimated twenty rivers account for two-thirds of the global plastic waste that reaches the oceans. But according to Schmidt, “for the first time, all available data on plastic in rivers have been collected and analysed to provide global numbers on riverine plastic transport.”

Apart from the plastic waste found floating in the open oceans, debris from between 50 to 200 km of coastal areas is accounted for, but plastic found in the rivers is not taken into consideration by scientists working on marine issues. This leaves out plastic found in areas away from the coasts and further inland, although rivers transport plastic debris into the sea.

Another example of plastic that slips through the net is known as the “missing plastic” problem. This is the discrepancy between the amount of plastic believed to be in the oceans and the debris actually encountered. “It is not clear yet whether particles sink or are fragmented to very small hardly detectable particles,” says Schmidt.

To address such discrepancies, the researchers compiled all the available data on plastic debris in rivers. For this, they identified patterns in concentrations of plastic and the time taken for them to be transported by the river. The amount of time taken for plastic debris to reach the ocean and levels of plastic depending on the characteristics of the catchment. As villages grow to become towns and towns metamorphose into cities to accommodate exploding populations, they directly have a bearing on the amount of plastic waste generated.

One of the garbage dumps in Mumbai from where plastic wastes flow into the sea. Photo by S. Gopikrishna Warrier.

Schmidt and team trawled through 1870 scientific papers and extracted 73 of them concerned with aquatic ecosystems to compile data on river plastic pollution. About 98.5% of the samples reported in the studies contained microplastics – particles less than 5 mm in diameter. More than half the samples (55%) contained macroplastics, particles more than 5 mm.

The researchers also estimated population size for 1494 catchments that drained into the seas. Taking the catchment and their population size, the team further calculated the mismanaged plastic waste generated per person every day in more than 230 countries that have river catchments draining into the sea. This is the ineptly disposed waste or garbage littered around.

The study estimates anywhere between 4.7 tonnes/year and 10 million tonnes/year of mismanaged plastic waste is generated in individual river catchments around the world. While Yangtze river in China carries the most amount of microplastic load, the San Gabriel that flows through Los Angeles carries the highest load of macroplastic.

Three rivers carrying the most plastic flow through India

Out of the ten rivers that drain over 90% of the total plastic debris into the sea globally, there are three flowing through India – the Indus, Ganga and Brahmaputra. While the Indus carries the second highest amount of mismanaged plastic debris to the sea, both Brahmaputra and Ganga together carry the sixth highest.

To address this situation, in 2016, Plastic Waste Management Rules were introduced by the MoEF&CC. The rules put the responsibility squarely on the manufacturers of plastic both to manage the waste system as well as to buy back the plastic waste generated.

Plastic waste from the sea brought in by the tide and stuck to mangrove plants in Kerala. Photo by S. Gopikrishna Warrier.

Mukherjee thinks manufacturers should look to make non-toxic alternatives to plastic as stipulated in the Waste Management Rules. Instead, she reckons, “we are recycling waste that was toxic in the first place and putting back materials that are equally toxic, like oxo-biodegradable plastic bags.” These bags shed into smaller pieces overtime and have been known to cause death in aquatic life.

PET bottles, polythene bags and food sachets are not the most difficult ones to recycle. “The most difficult to recycle, like shopping bags and industrial packaging material, are the ones responsible for choking rivers, lakes, or landfills,” says Mukherjee.

Everyday items made of plastics are not only ubiquitous in cities but have also become commonplace in villages. Siddharth Agarwal of Veditum Foundation has walked the length of Ganga from Gangasagar to Gangotri documenting plastic pollution along the river. Speaking to grocery store owners and villagers, he found plastic has replaced materials like earthenware and tin due to its convenience and durability.

Agarwal encountered plastic all along the river, in agricultural fields and in clogged drains, except for the stretch between Kanpur and Haridwar. He documented gutka packets, sachets of everyday consumables and discarded plastic from community events as the most polluting sources in the villages.

At the United Nations Environment Assembly organised in Nairobi, Kenya, in early December 2017, India along with 193 other nations signed a resolution to reduce marine plastic waste but stopped short of adhering to specific targets in reduction. The UN hopes countries keep their promises otherwise it fears there could be more plastic than fish in the oceans by 2050.